file1.rs

struct SharedState {
    data: HashMap<KeyType, ValueType>,
    msg_buf: Vec<Message<'static>>,
}

struct VecHolder<'a, 'b: 'a>(&'a mut Vec<Message<'b>>);

impl<'a, 'b: 'a> VecHolder<'a, 'b> {
    pub fn new<'o>(other: &'a mut Vec<Message<'o>>) -> Self {
        Self(unsafe { std::mem::transmute(other) })
    }

    pub fn inner<'d, 'e: 'd>(&'e mut self) -> &'d mut Vec<Message<'b>> {
        self.0
    }
}

impl<'a, 'b> Drop for VecHolder<'a, 'b> {
    fn drop(&mut self) {
        self.0.clear();
    }
}

impl SharedState {
    // other methods
    
    pub fn dispatch_events<'a>(
        &'a mut self,
    ) -> WsResult<UpdateTick> {
        let mut msg_buf: VecHolder<'a, 'a> = VecHolder::new(&mut self.msg_buf);
        // push a bunch of messages
        msg_buf.inner().push(/* messages */);
        handle_msgs(msg_buf.inner())?;
        Ok(self.latest_update)
    }
}